The present invention relates to a reclining angle adjustment device for adjusting the angle of inclination of the seat back of a reclining seat in an automobile, i.e., the reclining angle of the reclining seat.
One known reclining angle adjustment device comprises an intermediate gear plate having an outer gear, an upper arm having an inner gear meshing with the outer gear of the intermediate gear plate, an angularly movable shaft on which the intermediate gear plate and the upper arm are angularly movably mounted concentrically and eccentrically, respectively, thereon, a lower arm cooperating with a subplate in supporting the angularly movable shaft, a release lever for unlocking the intermediate gear plate from the lower arm for rough reclining angle adjustment, and a control handle for turning the angularly movable shaft through a transmission mechanism to effect fine reclining angle adjustment. The intermediate gear plate has a recess defined in an outer peripheral edge thereof, and the upper arm has a pin disposed in the recess. The upper arm can therefore be finely adjusted within a range between the front and rear edges of the recess which are engaged by the pin.
When the known reclining angle adjustment device is subject to vibration produced during travel of the automobile, for example, the inner gear tends to vibrate with respect to the outer gear for thereby allowing the angularly movable shaft to be temporarily rotated freely with the control handle. The seat back is caused to be tilted and hence the reclining angle thereof varies with time.